Green Sea Turtle (Chelonia mydas)

IDENTIFICATION

Size
– up to 1.5 m

Colour
– body is dark grey-green, outlined in white
– shell (carapace) has shades of green, brown, grey, black and yellow
– lower shell (plastron) is yellow-white
– black variants are black all over

Shell
– smooth, pointed at the rear
– scute behind the head is triangular shaped

Surface behaviour
– surfaces to breathe for a few minutes
– holds head above water, then slowly sinks back down

Group size / social behaviour
– solitary

Other characteristics
– largest of the hard-shelled sea turtles
– small head compared to other sea turtles

Can be confused with
– olive ridley sea turtle
– loggerhead sea turtle

NATURAL HISTORY

Green sea turtles are found throughout the North Pacific and range as far north as Alaska. They are more commonly seen in southern temperate waters around Mexico and Hawaii, but they sometimes show up in higher temperate latitudes when they drift in ocean currents during years with above-average sea temperatures.

There are two main green turtle breeding areas in the Northeast Pacific: Mexico (on the coast of Michoacan) and Hawaii (mainly at the French Frigate Shoals). Turtles in each region share similar patterns on their “plastron” (or lower shell) that can be used to trace their origin.

Green turtles are unique because their diet changes as they age. Juveniles are invertivores, feeding mainly on jellyfish and other invertebrates. Adults green turtles are the only turtles that are exclusive herbivores, feeding on kelp such as sea lettuce and algae. It is thought that this diet imparts a greenish colour to their skin and fat, giving them their name.

Individuals reach maturity around 25 years of age, after which females return to nesting beaches every 2-4 years to lay clutches of eggs that incubate for two months before hatching.

Green turtles worldwide are listed as endangered by the IUCN. Populations of green turtles have dramatically declined all over the world in the last hundred years, and some nesting sites have only a fraction of their original populations. The most important threat to green turtles is harvesting of eggs and adults from their breeding beaches, in spite of efforts to conserve these areas. Incidental catch in fishing gear is also a large problem for all sea turtles. Many green sea turtles populations are afflicted by a disease called fibropapillomatosis, which causes large tumours to grow on the head and face, interfering with feeding.

Green turtles are normally a tropical species but occasionally may follow a warm current northward and end up in BC or even Alaska waters. There are two forms within the same species: the tropical green turtle and the black turtle which is more often found closer to the North American coast.

STATUS IN CANADA

The green sea turtle is designated as Endangered worldwide by the World Conservation Union (IUCN) Red List. The assessment of green sea turtles by the IUCN is as follows:

Analysis of historic and recent published accounts indicate extensive subpopulation declines in all major ocean basins over the last three generations as a result of overexploitation of eggs and adult females at nesting beaches, juveniles and adults in foraging areas, and, to a lesser extent, incidental mortality relating to marine fisheries and degradation of marine and nesting habitats. Analyses of subpopulation changes at 32 Index Sites distributed globally show a 48% to 67% decline in the number of mature females nesting annually over the last 3–generations.

Green Sea Turtle
Green Sea Turtle
Green Sea Turtle
Green Sea Turtle
Black sea turtle found in Alaska, 2007
Drew Mathews
Black sea turtle found in Alaska, 2007
A study by Wild Whales predicted areas of entanglement risk to sea turtles in B.C.
Wild Whales
A study by Wild Whales predicted areas of entanglement risk to sea turtles in B.C.